Yes, it can be done... I did it in my 97.
Go to the bottom of this page
http://www.bimmernav.com/page8.html
the wiring diagram there will show you what to tap into (the white connection) Tap into the A/V audio and video inputs. I didnt buy the adapter. I used computer wiring connections to plug in RCA connectors. Not a perfect fit, but works perfectly.